Contents distributed via read-only recording media such as BD-ROMs can be classified in genres such as AV (Audio-Video) software including movie and music, and game software. However, with the sophistication of recent playback devices, some contents classified in the genre of AV software have an interactive function which game software generally has.
The interactive function is realized by incorporating information for the interactive function into a digital stream, which is constituted of moving picture portions and audio portions of the AV software. With this interactive function, it becomes possible to play a question video with use of the digital stream, receive an answer for the question from a user, and play an answer video when the answer from the user is correct, for instance.
However, although having such an interactive function, this type of content still belongs to the genre of AV software. Therefore, so-called user-skip is available while the content is played, just as normal AV software. The user-skip is one of functions specific to AV equipment (called “AV function”), which DVD playback devices and CD playback devices provide. With this function, playback can jump to predetermined positions (cue positions) on a digital stream according to instructions from the user (This jump operation is hereinafter called a “cue-up operation”). For instance, when a key allocated for the user-skip is pressed once by the user, the playback device starts playback from the first cue position that is nearest to the current playback position. When the key is pressed twice, the playback device starts playback from the second cue position that is second nearest to the current playback position, and when the key is pressed three times, the play back device starts playback from the third cue position that is third nearest to the current play back position.
For realizing the above-described interactive function, the start position of answer video is specified as a cue position by so-called marker information, and accordingly the playback process can jump from the question video to the answer video. However, the user might reach the answer video by repeating the skip operation because of this function. Basically, the answer video is designed to be played only when the user inputs the right answer for the question. If the video can be played back by repeating the skip operation, the poor operationality might give the user an impression that the content is only an extra of AV software. Of course, it is possible to set the playback device not to accept any AV function so that the user can not view the answer video by repeating the user-skip. However, this removes the advantage of AV software, and it is not recommendable for content creators.